title: Transmission electron microscopy study of microstructural properties and dislocation characterization in the GaN film grown on the cone-shaped patterned Al2O3 substrate.
abstract: Growing a GaN film on a patterned Al2O3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al2O3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al2O3 surfaces, i.e. the flat surface (FS), the inclined surface (IS) and the top surface (TS), respectively. Especially, the crystallographic orientation of R-GaN between the GaN film and the inclined Al2O3 substrate was identified as $[\overline 1 2\overline 1 0]_{{\rm GaN}} \hbox{//}[\overline 1 101]_{{\rm R - GaN} \,{\rm on}\,{\rm IS}} \hbox{//}[\overline 1 100]_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $, $(\overline 1 012)_{{\rm GaN}} \hbox{//}(1\overline 1 02)_{{\rm R - Ga}\,{\rm Non}\,{\rm IS}} \hbox{//}(\overline {11} 26)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $. In addition, a rotation by 9° between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0002)_{{\rm GaN}} $ and between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0006)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $ was found to reduce the lattice mismatch between the GaN film and the Al2O3 substrate. Many TDs in the GaN film were observed on the FS and TS of Al2O3. However, few TDs were observed on the IS. Most of the TDs generated from the FS of Al2O3 were bent to the inclined facet rather than propagating to the GaN surface, resulting in a reduction in the dislocation density. Most of the TDs generated from the TS of Al2O3 were characterized as edge dislocations.
authors.affiliation: Measurement and Analysis Team, National Nanofab Center, Daejeon 305-806, South Korea.
authors.forename: Jung Sik
authors.initials: JS
authors.lastname: Park
authors.forename: Jun-Mo
authors.initials: JM
authors.lastname: Yang
authors.forename: Kyung Jin
authors.initials: KJ
authors.lastname: Park
authors.forename: Yun Chang
authors.initials: YC
authors.lastname: Park
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Yoo
authors.forename: Chil Seong
authors.initials: CS
authors.lastname: Jeong
authors.forename: Jucheol
authors.initials: J
authors.lastname: Park
authors.forename: Yinsheng
authors.initials: Y
authors.lastname: He
authors.forename: Keesam
authors.initials: K
authors.lastname: Shin
keywords: GaN; dislocation; high-resolution transmission electron microscopy; interface; light-emitting diode; weak-beam dark field